The present invention relates to a digital soft wipe signal generating apparatus used in broadcasting appliances and the like.
In general, a soft wipe signal is produced as an analog form.
FIG. 1 is a schematic block diagram for showing an arrangement of a conventional soft wipe signal generating apparatus.
In FIG. 1, reference numeral 1 indicates an analog specific waveform generator for generating a signal 1a having a specific waveform such as a triangle waveform and a sawtooth waveform from either a horizontal synchronization (sync) signal, or a vertical sync signal. Reference numeral 2 indicates an amplifier for amplifying the signal 1a generated by this analog specific waveform generator 1 by a predetermined variable resistor.
Reference numeral 3 denotes a limiter for limiting upper and lower levels of the signal 1a amplified by the amplifier 2; reference numeral 4 represents a multiplier for synthesizing a picture signal "A" and a picture signal "B" based on an output signal 3a limited by the limiter 3, whereby a synthesized signal 4a is outputted therefrom.
Now, operation of the above-described prior art will be explained. The signal 1a obtained by the analog specific waveform generator 1 is of an analog type waveform, which produces a triangle waveform, a sawtooth waveform and a parabolic waveform.
The signal 1a generated by this analog specific waveform generator 1 is amplified to a predetermined level by the amplifier 2, and subsequently inputted into the limiter 3. This limiter 3 limits the upper and lower levels of the output signal from the amplifier 2 so that an output signal 3a produced by increasing the inclinations of the signal 1a is outputted.
The synthesized signal 4a between the picture signal A and the picture signal B is outputted from the multiplier 4 in such a manner that in response to this output signal, a ratio of synthesization between the picture signal A and the picture signal B is varied, and the inclination is established in the boundary between the picture signal A and the picture signal B, whereby the soft wipe signal may be produced.
However, in the above-described soft wipe signal generating apparatus, the soft wipe signal is produced by way of the analog method, both the amplification adjustment in the amplifier 2 is required and the limit level adjustment in the limiter 3 is also required. Furthermore, there is another problem that since capacitors and the like are employed in the analog specific waveform generator 1, this soft wipe signal generating apparatus is difficult to be manufactured in an integrated circuit.